Conventionally, for enhancing the safety of driving of automobiles, there have been proposed a number of apparatuses in which imaging means such as video cameras are mounted in a vehicle to monitor images of the surroundings of the vehicle and various kinds of information included in the images are retrieved and used.
Such apparatuses include a system of detecting the motion of an automobile nearby from a captured image signal with an optical correlation system and alerting the driver depending on the distance and speed of the automobile, a system of searching for a given position with respect to a “road region” in a recognized image to recognize a traffic sign, a system of displaying the outputs of cameras embedded in door mirrors or side mirrors of a vehicle with an image display device placed near the driver's seat in the vehicle to allow the driver to easily check the status of an oncoming vehicle and the status of an adjacent lane, and vehicle-mounted cameras capable of taking and displaying images of right and left blind spots and vehicle downward images simultaneously.
Such vehicle-mounted cameras are required to be independent of the climate conditions. For example, to attain an imaging device independent of the climate conditions, Patent Document 1 discloses a system in which the mirror portion of each door mirror of a vehicle is composed of a half mirror and a video lens equipped with an optical filter and an imaging device such as a CCD are placed inside the door mirror, and an image signal processed with a camera signal processing circuit placed in the interior of the vehicle is outputted to an image display device.
Patent Document 1 described above argues that the disclosed configuration can solve the problems related to the camera mount position that (1) a camera placed in the interior of a vehicle may disfigure the interior resulting in degrading the comfort and narrow the vision of the driver, (2) a camera placed in an engine compartment may cause a failure because the environment is extremely bad, and (3) a camera placed outside of a vehicle, such as on the side of a door and on the engine compartment, for example, will adversely affect the safety, the design and the performance such as aerodynamic resistance.
Patent Document 1: Japanese Laid-Open Patent Publication No. 5-294183 (FIG. 1)